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Hypertrophy: A guide to getting big

Hypertrophy: A guide to getting big


From the dawn of time scrawny teenage boys have travelled to Argos to buy York branded home dumbbell sets. Upon purchase, every day becomes chest and arms day. Swole is the goal.


Then 'functional fitness' poked it's head around the door and promised similar aesthetic gains AND better athletic performance. Since then, body building or hypertrophy, as it’s scientifically known, has been knocked off its perch.


However, increases in muscle mass are closely associated with long term health, injury prevention, strength and power development. So, it is an integral part to any training programme.


This article will provide you a no-nonsense understanding of what Hypertrophy is, how it is stimulated and how to train it.


What is Hypertrophy?


A muscle can increase in size either via Hyperplasia or Hypertrophy. The former is the increase in the number of myofibrils and the latter is an increase in the size of each individual myofibril. We will focus on Hypertrophy as Hyperplasia is more commonly observed rodents.  

If you are unsure of the structure of a muscle, Imagine it like a Russian doll set. Inside each larger body of muscle is a collection of smaller and small groups of fibres: 

> Inside a muscle is a collection of fascicles.

> Inside a Fascicle is a collection of muscle fibres

> Inside a muscle fibres is a collection of myofibrils

> Inside a myofibril is a collection of thick and thin filaments

 Muscle structure

We can sub categorise our muscle fibres into:

  • Type I (Slow twitch)
  • Type IIa (Fast & slow twitch)
  •  Type IIx (Fast twitch)


Hypertrophy can occur in two ways, either via an increase in the diameter or in length. You can achieve diameter or length increases after periods of resistance-based training.  Hypertrophy primarily occurs (but not exclusively) in type II fibres.



Why does the muscle grow?


As mentioned, it is primarily our Type II fibres that are sensitive to Hypertrophy. The role of these fibres is to generate high amounts of Force (strength). They are only activated when high levels of intensity are required (such as completing a heavy back squat or grinding out that last rep in a set of curls).


If a threshold is not met, then the motor unit (a neuron that attaches to a group of muscle fibres) will not be used. The body will conserve energy and use type I muscle fibres as they are more adept at low force, high repetition actions like long distance running.


To get massive-er we need to put in some effort to activate high threshold motor units and in turn use Type II fibres.


Initiating Muscle growth

Despite CT Fletcher's best efforts, we cannot "command our muscles to grow". A cascade of events needs to be initiated and the first step of this is referred to as, shockingly 'Initial stimulus'.

CT Fletcher

The 3 elements of initial stimulus are relatively well known in the fitness community, they are:

  • Mechanical tension
  • Metabolic stress
  • Muscle damage


Mechanical tension is when a muscle attempts to contract but forces (weight on the bar/gravity) are trying to prevent this and create a stretching force. For example, if you are doing a bicep curl you are trying to shorten the bicep muscle group but the dumbbell load is trying to lengthen the muscle.


The evidence that metabolic stress and muscle damage cause hypertrophy is shakey and in some parts illogical.


Chris Beardsley (Hypertrophy researcher/science demi-god) argues that mechanical tension is the primary driver of hypertrophy. Beardsley believes that metabolic stress only helps to improve mechanical tension conditions and that muscle damage is a by-product of mechanical tension.


Markers of all three are present after resistance training but only one stimulates the signalling to increase protein synthesis and muscle growth. Now, moving away from the physiological mechanisms, wtf does this all mean for YOUR training?


From the above, we now understand that:

  1. We need to initiate hypertrophy.
  2. Type II muscle fibres are the main fibres that will get larger.
  3. We can only access these fibres in high force and high effort exertions.


If you’d like to dive further into the scientific details of Hypertrophy, check out the below links:



If you are wanting to train for size, whether that is overall or just in a single muscle group.  Here are the big rocks that will make a difference.



When you first get started its likely that your advice will come from friends or the old gym guy who still wears a belt for lat-pull downs.  Sadly their advice is commonly polarising and points you towards either “light weights for building muscle” or “heavy weights for building muscle”. 


In reality the difference is negligible as long as you work close to 'failure'. Failure is simply when your muscles can no longer perform the task at hand from fatigue. 


When closing in on failure our muscles will be maximally recruiting and the speed in which we complete a rep will be slowing down dramatically. This is referred to as 'stimulated reps' - If you complete 20 reps and the last 4 are slow contractions* the stimulus is similar to a set of 6 with 4 slow reps.


In summary, load** is not vital BUT working close to failure is.


*It must be a ‘genuine’ slow contraction to be effective, manufacturing the speed yourself when you have more to give is not going to optimally recruit our muscle growing fibres.

**For inexperienced lifters, I would advise higher repetitions and lower load for safety and also the opportunity to practice the movements.



Volume is the number of repetitions multiplied by number of sets. Commonly in training people associate more as better. For hypertrophy an inexperienced 'lifter' can stimulate hypertrophy with a single set that is close to failure. We all remember 'noob gainz'.


As we become conditioned to particular exercises and our training age progresses, research indicates that greater volume is going to achieve better muscle growth.


The gains from Volume do have diminishing returns and hit a bit of a tipping point at 15 sets per muscle group per week. After this point, the inability to recover from training plays a role if we have simply stressed the body too much.


Other variables including, training frequency, rest periods, single joint vs multi joint play a much smaller role in the growth of muscle than we may think. They are important but the low hanging fruit is load and volume.



Muscle building programmes should primarily focus on high intention when lifting so that you are pushed close to volitional failure.


To reiterate, for beginners I would recommend that you focus on higher repetition sets to improve safety and opportunity for purposeful practice. As you become experienced you will need to progressively overload the system, with either greater load or greater volume in an exercise.


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